Presses are known for laminating together foils in packaging operations from U.S. Pat. Nos. 3,509,686, 3,817,801, and 5,307,692 as well as from U.S. Patent publications 2002/0023417 and 2004/0187443. As a rule such presses have a pair of vertically spaced dies, the lower one of which can be shifted vertically. A normally flat upper foil and a lower foil formed with an array of upwardly open and downwardly projecting pockets filled with items to be contained are passed through the press. The lower platen has an array of upwardly open recesses that fit loosely around the pockets of the lower foil. Both the platens are heated so that when they are pressed together, with the upper platen bearing downward on the upper face of the upper foil and the lower platen bearing upward on the lower face of the lower foil between the pockets, the confronting faces of the two foils are bonded together.
In order to squeeze out air bubbles and bring the platens together gently it is known also from German patent document 43,26,233 of M. Lübbers and R. Rütteroth to provide springs between the platens and their actuating plates. This arrangement puts an upper limit on the force the platens can exert so as not to damage fragile thermoplastic foils.
A problem with these arrangements is that occasionally the items in the pockets of the lower foil come out of these pockets. If the item is a soft candy or easily crushed pill, this merely means that the workpiece will be spoiled and a batch of rejects will be produced, as the laminating operation will be done. When, however, the item is something hard, for instance a metal bolt, the platens can be damaged and the workpiece can be pierced, requiring a time-consuming repair and cleanup operation.